By DAVID E. SANGER; Sheryl Gay Stolberg contributed reporting for this article.

Published: February 27, 2006

The Dubai company seeking to take over some terminal operations at six American ports formally asked the Bush administration on Sunday to conduct a deeper investigation into security concerns surrounding the deal. The request will leave President Bush in the politically delicate position of having to personally approve or disapprove the takeover.

The company, Dubai Ports World, which is controlled by the emir of Dubai, part of the United Arab Emirates, asked the government to conduct ''the full 45-day investigation authorized under U.S. law,'' an investigation that Mr. Bush and his advisers said last week was unnecessary. In a statement, the company said it was confident that the review of the American aspects of the $6.85 billion deal would reach the same conclusions that a lower-level study did in January, and that ''the security of the U.S. will not be harmed as a result of this acquisition.''

In a statement on Sunday, Edward H. Bilkey, the American-born chief operating officer of Dubai Ports World, also provided more details about his promise on Thursday to ''segregate'' the operations of the company in the United States. Mr. Bilkey said the company would create an American subsidiary to operate independently of executives in Dubai or in London until May 1, or until the new federal investigation concludes. The port terminals affected by the deal are in New York, Newark, Philadelphia, Baltimore, Miami and New Orleans.

The company's decision was prompted by discussions on Friday and Saturday with administration officials and Congressional leaders, who were seeking to quell the political storm over approval of the deal by the federal Committee on Foreign Investment in the United States, which reviews foreign investments that could affect national security.

In a statement on Sunday evening, the Treasury Department, which oversees the review process, said it ''welcomed'' the company's decision. It cited the fact that the deal was ''restructured'' as a reason for looking at it a second time. But in fact, very little has changed in the structure of the deal, as the company's own executives acknowledged on Friday.

The announcement by the company created an opening for Republican leaders, who had sharply criticized the White House as paying insufficient attention to the deal. The Senate majority leader, Bill Frist, and the chairman of the Senate Committee on Armed Services, John W. Warner of Virginia, said they were satisfied that the issue was now being handled properly.

''We cannot mess this deal up,'' said Mr. Warner, who spent hours with executives from the company over the weekend. He emerged to praise them on the quality of their port operations and said on the NBC program ''Meet the Press,'' ''We as the United States are dependent on countries like the U.A.E., Qatar, Bahrain, Kuwait, all of them there, to give us the support to fight this war on terrorism.''

In a statement on Sunday, Mr. Frist said he would recommend that the Senate await the outcome of the more extensive review before deciding on any legislative action.

But Democrats balked, insisting on their original demand that Congress should have the final say over the deal. Senator Charles E. Schumer, Democrat of New York, who joined a bipartisan group of senators on Friday in calling for a quick vote on legislation requiring a 45-day review, said Congress, not the White House, should make the final determination.

''We still believe that the report also has to go to Congress, that as much of it as possible ought to be public and that we would have the right of disapproval,'' Mr. Schumer said in an interview. ''That is part of our legislation. That is constitutionally valid; you can have the right of disapproval.''

Senator Hillary Rodham Clinton, another New York Democrat who was part of the bipartisan group, expressed qualified support for the company's offer, saying that the investigation should ''be carried out in a rigorous and independent manner with a report to the Congress giving us the opportunity to exercise our independent judgment.''

Similar sentiments were expressed by Senator Robert Menendez, Democrat of New Jersey, who appeared with his New York colleagues on Sunday at a news conference in Manhattan.

Representative Peter T. King, a New York Republican and chairman of the House Committee on Homeland Security, said he had supported Congressional approval of the deal to force Mr. Bush's hand. Now, Mr. King said, ''I'm keeping that in reserve. I'm certainly not ruling it out.''

Mr. Bush has vowed to veto any bill giving authority over the deal to Congress, rather than to the executive branch.

The White House had said Mr. Bush was unaware of the initial decision by his administration to approve the deal and was told by his chief of staff only over Presidents' Day weekend, after Republicans and Democrats began attacking it.

The new review, a 45-day formal investigation into potential national security threats, cannot be kept at arm's length by the president. Under the law, the committee will have to report its conclusions -- and any dissents -- to Mr. Bush, who will have 15 days to decide whether to approve the deal or to require the company to divest itself of some of the operations.